This invention relates to a novel method for producing a machine-readable coded marking in a surface of a workpiece.
U.S. Patent Application Ser. No. 041,091 filed May 21, 1979 by W. R. Miller describes an improved method for assembling parts for a CRT (cathode-ray tube) including providing at least one tube part, such as the glass faceplate, which has a unique machine-readable coded marking, such as a bar-code marking, on an external surface thereof. This marking is read one or more times by machine during the manufacturing of the tube. Each time it is read, a control signal is generated in response to the reading, and then the signal is used to initiate a local process for action with respect to the tube part. The local process may be one or more of selecting and assembling another part to the workpiece, a series of processing steps applied to the workpiece, a recording of a historical record, etc. The marking must be made reliably at low cost, must be readable reliably and at low cost and must survive the hostile environments of subsequent processing.
U.S. Patent Application Ser. No. 041,092 filed May 21, 1979 by P. M. Heyman discloses an improved workpiece which carries a machine-readable coded marking abraded into the surface of the workpiece. Also disclosed is a novel method whereby these abraded markings can be made on demand at relatively low cost and at relatively high rates of speed. Since the marking is abraded into the workpiece, it has substantially the same resistance to hostile environments as the workpiece itself. The abraded portions of the marking and the nonbraded portions therebetween have substantially different reflectances so that they can be read with commercial bar-code readers at low cost.
It is desirable to provide an alternative method for producing on demand a unique machine-readable coded marking in the surface of a workpiece, particularly one which, with the advance of technology may produce a better marking at lower cost.